title: Multicentre laboratory validation of the colorimetric redox indicator (CRI) assay for the rapid detection of extensively drug-resistant (XDR) Mycobacterium tuberculosis.
abstract: OBJECTIVE
  To perform a multicentre study to evaluate the performance of the colorimetric redox indicator (CRI) assay and to establish the MICs and critical concentrations of rifampicin, isoniazid, ofloxacin, kanamycin and capreomycin.
  
  
  METHODS
  The study was carried out in two phases. Phase I determined the MIC of each drug. Phase II established critical concentrations for the five drugs tested by the CRI assay compared with the conventional proportion method.
  
  
  RESULTS
  Phase I: a strain was considered resistant by the CRI assay if the MIC was ≥0.5 mg/L for rifampicin, ≥0.25 mg/L for isoniazid, ≥4.0 mg/L for ofloxacin and ≥5.0 mg/L for kanamycin and capreomycin. Sensitivity was 99.1% for isoniazid and 100% for the other drugs and specificity was 97.9% for capreomycin and 100% for the other drugs. Phase II: the critical concentration was 0.5 mg/L for rifampicin, 0.25 mg/L for isoniazid, 2.0 mg/L for ofloxacin and 2.5 mg/L for kanamycin and capreomycin giving an overall accuracy of 98.4%, 96.6%, 96.7%, 98.3% and 90%, respectively.
  
  
  CONCLUSIONS
  Results demonstrate that the CRI assay is an accurate method for the rapid detection of XDR Mycobacterium tuberculosis. The CRI assay is faster than the conventional drug susceptibility testing method using solid medium, has the same turnaround time as the BACTEC MGIT 960 system, but is less expensive, and could be an adequate method for low-income countries.
authors.affiliation: Mycobacteriology Unit, Institute of Tropical Medicine, Antwerp, Belgium. amartin@itg.be
authors.forename: Anandi
authors.initials: A
authors.lastname: Martin
authors.forename: Fabienne
authors.initials: F
authors.lastname: Paasch
authors.forename: Sven
authors.initials: S
authors.lastname: Docx
authors.forename: Krista
authors.initials: K
authors.lastname: Fissette
authors.forename: Belen
authors.initials: B
authors.lastname: Imperiale
authors.forename: Wellman
authors.initials: W
authors.lastname: Ribón
authors.forename: Liliana Andrea
authors.initials: LA
authors.lastname: González
authors.forename: Jim
authors.initials: J
authors.lastname: Werngren
authors.forename: Anna
authors.initials: A
authors.lastname: Engström
authors.forename: Girts
authors.initials: G
authors.lastname: Skenders
authors.forename: Pontus
authors.initials: P
authors.lastname: Juréen
authors.forename: Sven
authors.initials: S
authors.lastname: Hoffner
authors.forename: Patricia
authors.initials: P
authors.lastname: Del Portillo
authors.forename: Nora
authors.initials: N
authors.lastname: Morcillo
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Palomino
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D003124:Colorimetry / Q000379:methods*; D024901:Drug Resistance, Multiple, Bacterial; D054908:Extensively Drug-Resistant Tuberculosis / Q000175:diagnosis* / Q000382:microbiology; D006801:Humans; D007202:Indicators and Reagents / Q000378:metabolism; D008826:Microbial Sensitivity Tests / Q000379:methods; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification; D010084:Oxidation-Reduction
chemical_list: D000995:Antitubercular Agents; D007202:Indicators and Reagents